[PATCH 8/9] rhashtable: Supports for nulls marker
From: Thomas Graf
Date: Fri Jan 02 2015 - 17:01:27 EST
In order to allow for wider usage of rhashtable, use a special nulls
marker to terminate each chain. The reason for not using the existing
nulls_list is that the prev pointer usage would not be valid as entries
can be linked in two different buckets at the same time.
The 4 nulls base bits can be set through the rhashtable_params structure
like this:
struct rhashtable_params params = {
[...]
.nulls_base = (1U << RHT_BASE_SHIFT),
};
This reduces the hash length from 32 bits to 27 bits.
Signed-off-by: Thomas Graf <tgraf@xxxxxxx>
---
include/linux/list_nulls.h | 3 ++-
include/linux/rhashtable.h | 57 ++++++++++++++++++++++++++++++++++++++--------
lib/rhashtable.c | 37 ++++++++++++++++++++++++------
3 files changed, 79 insertions(+), 18 deletions(-)
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index 5d10ae36..e8c300e 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -21,8 +21,9 @@ struct hlist_nulls_head {
struct hlist_nulls_node {
struct hlist_nulls_node *next, **pprev;
};
+#define NULLS_MARKER(value) (1UL | (((long)value) << 1))
#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
- ((ptr)->first = (struct hlist_nulls_node *) (1UL | (((long)nulls) << 1)))
+ ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
/**
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index a1688f0..de7cac7 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -18,15 +18,32 @@
#ifndef _LINUX_RHASHTABLE_H
#define _LINUX_RHASHTABLE_H
-#include <linux/rculist.h>
+#include <linux/list_nulls.h>
#include <linux/workqueue.h>
+/*
+ * The end of the chain is marked with a special nulls marks which has
+ * the following format:
+ *
+ * +-------+-----------------------------------------------------+-+
+ * | Base | Hash |1|
+ * +-------+-----------------------------------------------------+-+
+ *
+ * Base (4 bits) : Reserved to distinguish between multiple tables.
+ * Specified via &struct rhashtable_params.nulls_base.
+ * Hash (27 bits): Full hash (unmasked) of first element added to bucket
+ * 1 (1 bit) : Nulls marker (always set)
+ *
+ * The remaining bits of the next pointer remain unused for now.
+ */
+#define RHT_BASE_BITS 4
+#define RHT_HASH_BITS 27
+#define RHT_BASE_SHIFT RHT_HASH_BITS
+
struct rhash_head {
struct rhash_head __rcu *next;
};
-#define INIT_HASH_HEAD(ptr) ((ptr)->next = NULL)
-
/**
* struct bucket_table - Table of hash buckets
* @size: Number of hash buckets
@@ -55,6 +72,7 @@ struct rhashtable;
* @hash_rnd: Seed to use while hashing
* @max_shift: Maximum number of shifts while expanding
* @min_shift: Minimum number of shifts while shrinking
+ * @nulls_base: Base value to generate nulls marker
* @locks_mul: Number of bucket locks to allocate per cpu (default: 128)
* @hashfn: Function to hash key
* @obj_hashfn: Function to hash object
@@ -69,6 +87,7 @@ struct rhashtable_params {
u32 hash_rnd;
size_t max_shift;
size_t min_shift;
+ u32 nulls_base;
size_t locks_mul;
rht_hashfn_t hashfn;
rht_obj_hashfn_t obj_hashfn;
@@ -100,6 +119,24 @@ struct rhashtable {
bool being_destroyed;
};
+static inline unsigned long rht_marker(const struct rhashtable *ht, u32 hash)
+{
+ return NULLS_MARKER(ht->p.nulls_base + hash);
+}
+
+#define INIT_RHT_NULLS_HEAD(ptr, ht, hash) \
+ ((ptr) = (typeof(ptr)) rht_marker(ht, hash))
+
+static inline bool rht_is_a_nulls(const struct rhash_head *ptr)
+{
+ return ((unsigned long) ptr & 1);
+}
+
+static inline unsigned long rht_get_nulls_value(const struct rhash_head *ptr)
+{
+ return ((unsigned long) ptr) >> 1;
+}
+
#ifdef CONFIG_PROVE_LOCKING
int lockdep_rht_mutex_is_held(struct rhashtable *ht);
int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash);
@@ -157,7 +194,7 @@ void rhashtable_destroy(struct rhashtable *ht);
*/
#define rht_for_each_continue(pos, head, tbl, hash) \
for (pos = rht_dereference_bucket(head, tbl, hash); \
- pos; \
+ !rht_is_a_nulls(pos); \
pos = rht_dereference_bucket((pos)->next, tbl, hash))
/**
@@ -180,7 +217,7 @@ void rhashtable_destroy(struct rhashtable *ht);
*/
#define rht_for_each_entry_continue(tpos, pos, head, tbl, hash, member) \
for (pos = rht_dereference_bucket(head, tbl, hash); \
- pos && rht_entry(tpos, pos, member); \
+ (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
pos = rht_dereference_bucket((pos)->next, tbl, hash))
/**
@@ -209,9 +246,9 @@ void rhashtable_destroy(struct rhashtable *ht);
*/
#define rht_for_each_entry_safe(tpos, pos, next, tbl, hash, member) \
for (pos = rht_dereference_bucket((tbl)->buckets[hash], tbl, hash), \
- next = pos ? rht_dereference_bucket(pos->next, tbl, hash) \
- : NULL; \
- pos && rht_entry(tpos, pos, member); \
+ next = !rht_is_a_nulls(pos) ? \
+ rht_dereference_bucket(pos->next, tbl, hash) : NULL; \
+ (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
pos = next)
/**
@@ -228,7 +265,7 @@ void rhashtable_destroy(struct rhashtable *ht);
#define rht_for_each_rcu_continue(pos, head, tbl, hash) \
for (({barrier(); }), \
pos = rht_dereference_bucket_rcu(head, tbl, hash); \
- pos; \
+ !rht_is_a_nulls(pos); \
pos = rcu_dereference_raw(pos->next))
/**
@@ -260,7 +297,7 @@ void rhashtable_destroy(struct rhashtable *ht);
#define rht_for_each_entry_rcu_continue(tpos, pos, head, tbl, hash, member) \
for (({barrier(); }), \
pos = rht_dereference_bucket_rcu(head, tbl, hash); \
- pos && rht_entry(tpos, pos, member); \
+ (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member); \
pos = rht_dereference_bucket_rcu(pos->next, tbl, hash))
/**
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 312e343..cbad192 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -28,6 +28,9 @@
#define HASH_MIN_SIZE 4UL
#define BUCKET_LOCKS_PER_CPU 128UL
+/* Base bits plus 1 bit for nulls marker */
+#define HASH_RESERVED_SPACE (RHT_BASE_BITS + 1)
+
enum {
RHT_LOCK_NORMAL,
RHT_LOCK_NESTED,
@@ -86,7 +89,7 @@ static u32 obj_raw_hashfn(const struct rhashtable *ht, const void *ptr)
hash = ht->p.hashfn(ptr + ht->p.key_offset, ht->p.key_len,
ht->p.hash_rnd);
- return hash;
+ return hash >> HASH_RESERVED_SPACE;
}
static u32 key_hashfn(struct rhashtable *ht, const void *key, u32 len)
@@ -95,6 +98,7 @@ static u32 key_hashfn(struct rhashtable *ht, const void *key, u32 len)
u32 hash;
hash = ht->p.hashfn(key, len, ht->p.hash_rnd);
+ hash >>= HASH_RESERVED_SPACE;
return rht_bucket_index(tbl, hash);
}
@@ -111,7 +115,7 @@ static struct rhash_head __rcu **bucket_tail(struct bucket_table *tbl, u32 n)
struct rhash_head __rcu **pprev;
for (pprev = &tbl->buckets[n];
- rht_dereference_bucket(*pprev, tbl, n);
+ !rht_is_a_nulls(rht_dereference_bucket(*pprev, tbl, n));
pprev = &rht_dereference_bucket(*pprev, tbl, n)->next)
;
@@ -164,6 +168,7 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
{
struct bucket_table *tbl;
size_t size;
+ int i;
size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
tbl = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
@@ -180,6 +185,9 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
return NULL;
}
+ for (i = 0; i < nbuckets; i++)
+ INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
+
return tbl;
}
@@ -221,7 +229,7 @@ static void hashtable_chain_unzip(const struct rhashtable *ht,
/* Old bucket empty, no work needed. */
p = rht_dereference_bucket(old_tbl->buckets[old_hash], old_tbl,
old_hash);
- if (!p)
+ if (rht_is_a_nulls(p))
return;
new_hash = new_hash2 = head_hashfn(ht, new_tbl, p);
@@ -252,8 +260,8 @@ static void hashtable_chain_unzip(const struct rhashtable *ht,
/* Find the subsequent node which does hash to the same
* bucket as node P, or NULL if no such node exists.
*/
- next = NULL;
- if (he) {
+ INIT_RHT_NULLS_HEAD(next, ht, old_hash);
+ if (!rht_is_a_nulls(he)) {
rht_for_each_continue(he, he->next, old_tbl, old_hash) {
if (head_hashfn(ht, new_tbl, he) == new_hash) {
next = he;
@@ -369,11 +377,15 @@ int rhashtable_expand(struct rhashtable *ht)
*/
complete = true;
for (old_hash = 0; old_hash < old_tbl->size; old_hash++) {
+ struct rhash_head *head;
+
old_bucket_lock = bucket_lock(old_tbl, old_hash);
spin_lock_bh(old_bucket_lock);
hashtable_chain_unzip(ht, new_tbl, old_tbl, old_hash);
- if (old_tbl->buckets[old_hash] != NULL)
+ head = rht_dereference_bucket(old_tbl->buckets[old_hash],
+ old_tbl, old_hash);
+ if (!rht_is_a_nulls(head))
complete = false;
spin_unlock_bh(old_bucket_lock);
@@ -498,6 +510,7 @@ static void rht_deferred_worker(struct work_struct *work)
void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj)
{
struct bucket_table *tbl;
+ struct rhash_head *head;
spinlock_t *lock;
unsigned hash;
@@ -508,7 +521,12 @@ void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj)
lock = bucket_lock(tbl, hash);
spin_lock_bh(lock);
- RCU_INIT_POINTER(obj->next, tbl->buckets[hash]);
+ head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
+ if (rht_is_a_nulls(head))
+ INIT_RHT_NULLS_HEAD(obj->next, ht, hash);
+ else
+ RCU_INIT_POINTER(obj->next, head);
+
rcu_assign_pointer(tbl->buckets[hash], obj);
spin_unlock_bh(lock);
@@ -709,6 +727,7 @@ static size_t rounded_hashtable_size(struct rhashtable_params *params)
* .key_offset = offsetof(struct test_obj, key),
* .key_len = sizeof(int),
* .hashfn = jhash,
+ * .nulls_base = (1U << RHT_BASE_SHIFT),
* };
*
* Configuration Example 2: Variable length keys
@@ -741,6 +760,9 @@ int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
(!params->key_len && !params->obj_hashfn))
return -EINVAL;
+ if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
+ return -EINVAL;
+
params->min_shift = max_t(size_t, params->min_shift,
ilog2(HASH_MIN_SIZE));
@@ -974,6 +996,7 @@ static int __init test_rht_init(void)
.key_offset = offsetof(struct test_obj, value),
.key_len = sizeof(int),
.hashfn = jhash,
+ .nulls_base = (3U << RHT_BASE_SHIFT),
.grow_decision = rht_grow_above_75,
.shrink_decision = rht_shrink_below_30,
};
--
1.9.3
--
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